Re: starting flies?
Following William's sage advice, pretty big bass will take pretty small flies as long as you put your fly somewhere the bass will see it. I personally like to fish a smaller fly to primarily target bluegills, and find I catch at least my fair share of bass in doing so.
If you want to target the bass, you might be better off fishing a larger fly, the bass will be able to see it from a greater distance, so it could up your catch rate of bass. As flies get larger and larger, it takes more energy to deliver them, so at least for me, fishing smaller flies is a bit more pleasant.
The good news is, as a rule, neither bass or bluegill are particularly fussy about what they will eat. Again getting back to William's point, get the fly close to them, at least some of them will take it.